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MEPS prepress abstract   -  DOI:

Biological traits of benthic macrofauna show size-based differences in response to bottom trawling intensity

CiarĂ¡n McLaverty*, Grete E. Dinesen, Henrik Gislason, Mollie E. Brooks, Ole R. Eigaard

*Corresponding author:

ABSTRACT: Bottom trawling results in widespread impacts to the structure and composition of benthic communities. Although an ecosystem approach to fisheries management aims to conserve marine biodiversity and ecosystem function, there remains a lack of empirical evidence regarding the effects of trawling on benthic functional properties. Here, we examine the sensitivity of benthic macrofauna communities to trawling using their biological traits, and compare trait responses across size-categories and survey types. 84 benthic soft-sediment samples were collected by Van Veen grab (0.1m2) in the Kattegat in 2016, and complemented with 827 HAPS cores (0.0143m2) gathered over a long-term monitoring programme between 2006 and 2013. By analysing trait response in three size categories (small: 1-4 mm fraction, large: ≥4 mm fraction, and full community: all individuals combined), we demonstrate a size-dependent effect of trawling on benthic trait composition, where the traits of large-bodied fauna (≥4mm) were more sensitive. Specifically, larger sessile, deep-living, suspension-feeding, tube-dwelling, subsurface deposit feeding, burrow-dwelling, and long-lived (≥10 years) individuals were among the most affected. Our results based on large fauna were largely in agreement with trait responses observed in the multi-year monitoring data. This would suggest that trait data gathered from a targeted one-off sampling event can convey information on both acute (short-term) and chronic (long-term) trawling impacts. Given that most trawling impact assessment do not consider size-based effects, we outline how size-separating the community can be used to improve the detectability of trawling impacts, and provide new insights into the functional impacts of fishing on the seabed.